Many enterprises have moved from telephony services using the Public Switched Telephone Network (PSTN), provided by a traditional telephone company, to telephony services using the Internet Protocol (IP), provided by an IP Telephony service provider. Such services are commonly known as Voice over IP (VoIP) or IP Telephony.
Now that an IP network, such as the public Internet or a private IP network, can be used as a backbone rather than the limited PSTN, IP Telephony has the capability of providing advanced features such as video conferencing, call recording, and call forwarding, to name a few. However, the primary use of IP Telephony service is still to connect IP Telephony callers to PSTN callers.
For this reason, the signaling infrastructure (e.g., proxies, application servers, etc.) utilized by the IP telephony service provider is designed to allow many different types of endpoints to access the less feature-rich services provided by PSTN gateways. The service provider often manipulates and/or normalizes traffic. Such manipulation may include, for example, translation to a least common denominator codec, manipulating/removing certain SIP headers, etc. Such manipulations can interfere with advanced IP telephony services that serve to differentiate IP telephony from PSTN telephony.